You think that at dinner table the choices belong to you, that being a sweet tooth or meat eater is something you chose, but scientists believe that in fact what you engulf has a lot to do with something ancient inside all of us. "In fact, our food preferences are an outgrowth of the survival instincts we share with other animals. In the end, we aren't much different from rats." said Thomas Pritchard, associate professor of neural and behavioral sciences.

"Rats cannot vomit. When a rat eats something, it's forever", he said.

That's why a rat encountering for the first time an unfamiliar taste, "will nibble at the food and walk away," Pritchard noted. The animal then will wait up to 24 hours to see if the food is poisonous, making it sick, and if it does, the rat will never touch the item in the future.

The neophobia (fear of novelty) and the long term memories taste-illness after just one bite could explain the success of the rats in both wild and human settlements. Thus, rats are more picky eaters than imagined.

Scientists believe the humans developed a taste for food in a similar manner. "The senses of taste and smell evolved to help us identify nutritious foods and poisonous substances," Pritchard said. "Acidity for example, is usually an indication of spoilage, while bitterness signals our brain to think "poison." Even the common "sweet tooth" may be rooted in survival instinct. Carbohydrates, typically sweet, are a vital energy source to a wild animal continuously on the go. The evolved ability to associate sweetness with energy may lie behind our present-day preferences for ice cream and candy bars," Pritchard speculates.

Modern humans get their food in a short drive to the supermarket, while our tastes evolved in conditions of hard foraging, that consumed large amounts of energy, and made us picky eaters for items that delivered us larger quantities of energy. But this turned against us in the current lifestyle. "Taste and smell, the two senses that have worked so well to get us through the times when food was not conveniently available, may now be working against us," said Pritchard.

Abundant sources of carbohydrates are achieved with difficulty in nature, and salt is scarce, but now our pervasive taste for sweet and salty food leads to new metabolic problems, such as obesity, heart disease and diabetes. "That's the price we pay for attending to the hedonic properties of food instead of the long term health consequences of our diet," he said.

Along with sweet and bitter, Humans perceive five tastes: sweet, bitter, salty, sour, and umami ("savory" in Japanese). "These basic taste qualities, in combination with the senses of smell and touch, allow us to recognize thousands of different flavors", Pritchard says.

But to the physiological factors we can add the psychological one, molding our taste. "Children develop food preferences through exposure and association," Pritchard explains. Early and often contact with chili peppers increases the odds of liking it as adults. We also associate from childhood particular foods and flavors with sickness, happiness, rage, or stress, sometimes for the rest of our lives. "In fact, research confirms that the five basic tastes are at the vanguard of food preference."

"Taste information goes through the nervous system in a serial fashion," he said.

The primary tastes may be located in the hypothalamus, but more sophisticated aspects involving memory, emotion, and motivation (as the diet we make when practicing sports or slimming) are located in the more recently evolved regions in the cortex.

Basic food preference is in our genes, but choosing ketchup over mayonnaise is something connected to experience.